"Sorry this naming business has taken so long! We had a bit of a curveball when we announced your name to our family, as someone pointed out, it's possibly illegal to name you that in Australia," Alexander-Johnston wrote in the caption addressed to her youngest son.

"We tried to change it. 'Disco' even came back into play! But nothing else felt right for you as a Libra, with a (very sensible and grounded) Capricorn moon."

"So Citizen you are, and always will be- a Citizen of the world."

She also joked that if little Citizen had any issues with his name in his teen years, he could always go by the nickname 'Zen' while "hanging in the garage punching bongs with 'Benji and the crew'."